scsi: ufs: core: Add helpers to pause and resume command processing

scsi: ufs: core: Add helpers to pause and resume command processing

In preparation for supporting TX Equalization refreshing, introduce helper
functions to safely pause and resume command processing.

ufshcd_pause_command_processing() ensures the host is in a quiescent state
by stopping the block layer tagset, acquiring the necessary locks
(scan_mutex and clk_scaling_lock), and waiting for any in-flight commands
to complete within a specified timeout.

ufshcd_resume_command_processing() restores the host to its previous
operational state by reversing these steps in the correct order.

Reviewed-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Can Guo <can.guo@oss.qualcomm.com>
Reviewed-by: Peter Wang <peter.wang@mediatek.com>
Link: https://patch.msgid.link/20260325152154.1604082-7-can.guo@oss.qualcomm.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>